In a large bowl, toss the apples with lemon juice, granulated sugar, maple syrup, cornstarch, 1 teaspoon of cinnamon, and the salt until well coated.
In another bowl, combine the gluten-free oats, almond flour, 1/2 teaspoon of cinnamon, the brown sugar, and nutmeg.
Pour the melted butter over the dry ingredients and mix until the mixture is crumbly.
Preheat your oven to 350°F. Place the apple mixture in a greased baking dish. Evenly sprinkle the topping over the apples. Bake for 20 minutes covered with foil.
Remove foil and bake 20-25 minutes longer, or until the topping is golden and the apples are bubbly.
Serve with a scoop of vanilla ice cream or a dollop of whipped cream.